The present invention relates to a new method and apparatus for simulating and treating malignant tumors and, especially, multiple malignant tumors present throughout a patient's body. Specifically, the invention permits a number of anatomical regions, including the head, neck, thorax, abdominal and pelvic cavities, and some lower extremity areas, to be treated with beams of precision directed, therapeutic radiation while the patient remains comfortably supported in the same upright position.
Modern radiation therapy is an effective modality for treating various carcinomic diseases. More than one-half of all cancer patients in the United States receive some form of curative or palliative radiation treatment, with approximately 500,000 patients being treated annually. The majority of patients receiving external beam radiation therapy are treated on an isocentrically mounted treatment table, or patient support assembly (PSA), provided as standard equipment on most current accelerators and cobalt teletherapy treatment machines. In such systems, the radiation source is mounted on a gantry which rotates around a prone or supine patient. This method provides flexibility in setup and comfort for most patients, however, there are a variety of clinical situations in which patients can benefit from being treated in an upright sitting position.
Many patients, for example those who have carcinoma of the bronchus, superior vena cava syndrome, or malignant pleural effusions, often complain of dyspnoea (shortness of breath) of sufficient degree to make lying flat difficult or sometimes impossible. Children, especially, do not tolerate the recumbent position easily. For other patients who have varying degrees of dyspnoea, but who can manage to lay flat for short periods of time, treatment in the sitting position is often more comfortable. Patients having excess salivation, severe kyphosis and those with head and neck malignancies whose shoulders must be depressed in order to exclude them from the treatment fields are also better treated in a sitting position.
Patients with large mediastinal masses, e.g. Hodgkin's Disease, may preferably be treated in the sitting position. Mediastinal tumors often widen in the recumbent position, resulting in the irradiation of a larger volume of normal underlying lung. With patients seated upright, the effect of gravity on the tumor mass tends to elongate the disease, thus minimizing its frontal profile mass. The amount of lung which can be shielded in this position is appreciably greater than when the patient is lying down, thus greatly decreasing the morbidity of the treatment.
Hodgkin's patients with large breasts receiving mantle irradiation may likewise benefit from treatment in a sitting position. In the recumbent position, the breast tends to intrude into the axillary regions and, thus, may receive undesirable radiation exposure during treatment of the axilla. In the sitting position, however, the breast tends to fall away from the axillary regions and is, thus, more easily shielded. Similarly, other patients with large breasts, receiving irradiation for breast cancers, have been found difficult to treat in the supine position since the breasts tend to spread out over a larger area than one would like to encompass in the treatment fields. In the seated position the breasts can be more easily contained to the required area and may be provided with some support underneath.
The sitting position is also desirable for treating brain tumors in that it allows the head to be supported using bite-block or other unobstructive immobilization techniques so as to improve access to the head. See C. Karzmark, et al., Br. J. Radiol., 53:926-28 (1975). With the patient supported in this manner, any portion of the brain, or indeed any tumor in the head or neck, can be easily treated with therapeutic radiation.
Despite the benefits to be gained from treating patients in a seated upright position, the technique does present certain difficulties. In order to minimize exposure of healthy tissue to high level dosages of radiation, for instance, modern radiotherapy treatment utilizes multiple beams of sharply collimated, high-energy radiation which are directed to intersect the tumor site at various angles. In this manner the volume of normal tissue raised to full tumor dosage can be restricted to an area immediately surrounding the geometrical limits of the malignant tissue (although a larger volume of normal tissue is irradiated to a lower dosage). Multiple portals are often used in combination with extensive field shaping and beam modification devices to achieve optimal dose distribution throughout the tumor. Working with these sharply collimated beams of high energy radiation calls for great accuracy in tumor localization, in beam directing, and in the setting up and restraining of the patient, especially when the tumor site is located in or near vital organs. Moreover, radiotherapy treatment is seldom accomplished in a single session, and usually requires several treatment sessions conducted over a period of time ranging from a few weeks to a few months. In order to ensure consistent results, it is necessary to accurately duplicate the treatment setup during each subsequent session.
Unfortunately, the development of precision treatment chairs with special features for executing sophisticated treatment plans has lagged behind that of treatment tables. The earliest radiotherapy treatment chairs consisted of little more than a flat sitting surface supported by a hydraulic pump and piston. Various support devices, such as adjustable back rests, headrests, and chin-rests, could be attached to the chair as needed to help support the patient in an upright position. The whole assembly was typically mounted on ball-castors so that the patient could be moved in a horizontal plane and rotated for placement in the radiation field. See, e.g., G. Wiernick, Br. J. Radiol., 34:676-78 (1961); Y. Allain et al., J. de Radiol. et d'Electrol., 52:189-92 (1971); and G. Watson et al., Br. J. Radiol., 44:317-19 (1971). Although this design provided adequate mobility for positioning the patient in the radiation field, precise tumor localization was not possible due to the inherent limitations of the ball-castors. Because the force required to overcome static friction in the ball-castors is greater than the corresponding dynamic friction force, a sling-shot effect is created making precision adjustment of the chair exceedingly difficult.
Other radiotherapy chair designs, although capable of precision adjustment, lacked the repeatability necessary to efficiently execute multiple treatment sessions. A chair developed by Boag and Hodt, for instance, provided precision translational adjustment to a maximum of 5 cm from a selected central position. The chair itself was free to move on ball-castors and could be secured on the treatment floor by three locking pads. Once the chair was secured, the seat portion could be precisely adjusted in the radiation field for tumor localization. Rotation was accomplished by locking the rear pad and using it as the axis of rotation. The location of the chair on the treatment floor, however, was not easily duplicated during subsequent treatment sessions See, J. Boag and H. Hodt, Br. J. Radiol., 44:316-17 (1971).
Another difficulty encountered in treating patients in the seated position is that the amount of physical structure required to support a patient in an upright position often obstructs or, at best, substantially reduces access to certain anatomical regions, especially the lower abdominal and pelvic cavities, which may require treatment. For example, a chair designed by Morrison et al. utilized an attachable back support and footrest assembly to convert a custom treatment table into a chair-like support. The positioning capability of the table itself provided adequate translational and rotational adjustment necessary for precise tumor localization. But, the additional back support structure blocked posterior fields and the table obstructed treatment of the pelvic and lower abdominal cavities, making the table inconvenient for general clinical use. See R. Morrison et al., Br. J. Radiol., 29:177-86 (1956).
Miller et al. describes a free-standing isocentric chair for simulation and treatment of radiation therapy patients. The chair consists of three distinct components: a base-plate, a translation/elevation mechanism, and a seat. Rotation is provided by a centrally mounted turntable supported by specially constructed ball bearings. Vertical motion is provided by a scissors-type mechanism, in combination with a spring-loaded supplemental booster at the low end of travel. The seat consists simply of a rectangular aluminum plate having four attachment points, one on each corner. The seat is apparently designed to function as a "tool platform" for receiving various standard and customized patient support and immobilization devices. Adjustable lateral "restrictors" are used to center the patient on the seat, at the hips. Although the chair may provide ample mobility and adjustment capability, the extensive support structure, particularly the large rectangular seat and lateral restrictors, blocks access to the pelvic and lower abdominal cavities which may require treatment. See R. Miller et al., Int'l. J. Rad. Onc. Biol. Phys., 2:464-473 (1991). The seat consists simply of a rectangular aluminum plate having four attachment points, one on each corner.
Varian Associates, Radiation Division, Palo Alto, CA, currently manufactures a treatment chair for optional attachment to its own radiotherapy treatment table design. The Varian chair is relatively simple in that it utilizes the horizontal, vertical, and rotational motions of the treatment table for precise tumor localization. The seat, foot-rest, arm-rests, head holder and bite-block are all supported by a central column which attaches to and extends up from the end of the treatment table. Unfortunately, this central column blocks beam access from behind the patient, making posterior treatment virtually impossible to administer. See, Varian Radiotherapy Accessories Catalog: Radiotherapy Treatment Chair, Varian Associates, Radiation Division, Palo Alto, CA., 94303.
The equipment heretofore available for treating patients in an upright position has been heavy, difficult to handle, and expensive. One of the more sophisticated radiotherapy treatment chairs, for example, is that designed by Karzmark et al. This chair, designed primarily for treating head and neck tumors, incorporates two axes of rotation in addition to longitudinal and lateral translation. A rotating turntable supports an x-y translation mechanism to which is attached a central support column. The seat, armrests, head support, and bite-block, attach to the central support column which can also rotate about its central axis. All adjustments are motor driven, using a remote pendant. The mechanical equipment and motors are installed beneath the floor in order to keep the height of the chair below a non-isocentrically mounted radiation source. Vertical adjustment is accomplished by adjusting the height of the radiation source. The substantial size and weight of the chair, however, prevents easy substitution of a treatment table when treatment in the supine position is required. See C. Karzmark et al., Br. J. Radiol., 53:1190-94 (1980). Similarly, the Varian chair, described above, weighs over 150 pounds, also making it less than ideal for clinical use. Not only is the chair unwieldy, but its weight, in combination with that of the patient, can overstress the motors which operate the treatment table.
Simulation is an important step in planning and verifying a patient's treatment fields prior to initiating radiotherapy. The simulator is typically configured to emulate the final treatment setup, except that low-energy radiation is used to obtain a radiograph or tomograph of the tumor site. Ideally a single chair could be used to support a patient during both simulation and treatment. This permits simulation of the therapy to be performed with the patient in the same position as during the therapy, which is important because of the above-mentioned anatomical changes.
There remains a current need for a lightweight and inexpensive radiotherapy treatment chair that can be used in combination with existing radiotherapy treatment machines and simulators to unobstructively support a patient in a stable and reproducible upright position during treatment with therapeutic radiation.